An electric boring tool such as a hammer drill driven by an electric motor is used for forming holes in work material (work) such as concrete and brick by providing rotational force, hammer force or both to a tip tool such as a drill bit using an electric motor. Such an electric boring tool is also used for an operation to trim such a hole. However, there is a problem where it is easy for damage to occur in the vicinity of an opening for a hole when creating a hole in brittle work such as concrete or brick.
In view of this, patent literature 1 discloses a technique wherein an applied voltage proportional to an extent of pulling (extent of operation) of a switch trigger of an electric boring tool is taken as a control signal to rise as the extent of pulling of the trigger rises. This then results in motor speed being made to increase in proportion to the extent of pulling of the trigger. With this kind of control, the speed of the motor is prevented from increasing abruptly by the operator keeping the extent of pulling of the switch trigger small when starting operation so as to maintain a low speed. This means that positioning of the tip tool or working by the tip tool with respect to the work becomes easier for operations such as making holes or cutting and damage to the work is prevented.